Strut-type suspension is well known in motor vehicles wherein a telescopic strut normally incorporating an hydraulic damper is used as one locating member for a motor vehicle wheel. The most common form of strut suspension is the so-called McPherson strut where the suspension spring is located concentrically around the telescopic strut which has an upper mounting point to the vehicle chassis in a tower located above the front wheel arch and protruding into the engine bay of the motor vehicle. The lower end of the strut is typically further located by a transverse link and a fore and aft or drag link.
The wheel alignment of a motor vehicle, and particularly the front wheel alignment is important to the safe handling of the vehicle and to preventing wear on the tires. There are many times in the life of a vehicle when it is necessary or desirable to adjust the castor and camber of a motor vehicle wheel either due to normal wear and tear or to some form of minor damage such as the striking of kerbs or other obstacles. On many motor vehicles fitted with McPherson strut suspensions, this adjustment is often difficult to perform as the motor vehicle manufacturer provides little or no mechanism for relocating the upper end of the strut where it mounts into the vehicle chassis. It is often necessary to relocate the mounting point of the upper end of the strut to achieve the desired castor and camber settings.
It is common for the upper end of a McPherson strut to be secured to the chassis member by way of three vertical studs located on a pitch circle and passing from a flange at the upper end of the strut through aligned holes in the vehicle chassis member. Some manufacturers have provided a degree of adjustment by locating the axis of the strut off-center from the pitch circle of the studs so that disengaging the studs from the holes in the vehicle chassis member, rotating the strut and re-engaging the studs through the holes will relocate the axis of the strut relative to the vehicle chassis member. This is however an extremely coarse adjustment which only permits the top end of the strut to be located in three defined positions. Furthermore, if it is required to alter the camber of the suspension without affecting the castor (or visa versa), this adjustment is not possible using the mounting described above.